TransHab (short for "Transit Habitat") is the first space inflatable module designed by the National Aeronautics and Space Administration (NASA). It was conceived as a technology capable of supporting a crew of six on an extended space journey, such as a six-month trip to Mars. During its development in 1997-2001 at NASA's Johnson Space Center in Houston, Texas, TransHab was considered for use on International Space Station "Alpha" as a habitation module for two reasons: first, because of its superior ability to support crew needs, and second, to test it for possible use on a human mission to Mars.
TransHab was first conceived in 1997 by a team of engineers and architects at the Johnson Space Center. A space human factors group was asked to join the design team in developing the best size and layout for the spacecraft. Based in part on psychological, social, and operational lessons learned from earlier American and Russian missions, the team recommended a three-level internal layout with crew quarters isolated at the center; mechanical systems grouped together in a separate "room"; and exercise and hygiene situated on a different level from the public functions of kitchen, dining and conferencing. The total volume is over 342 cubic meters.
All spacecraft flown up until now have been of an exoskeletal type—that is, its hard outer shell acts both as a pressure container and as its main channel for structural loading. This includes the rest of Alpha, which is currently under construction in low Earth orbit at about 250 miles above the Earth.
By contrast, TransHab is the first endoskeletal space habitat, consisting of a dual system: a light, reconfigurable central structure and a deployable pressure shell. The shell is so resilient because it is made of several layers, each with its own specific purpose. Principal among these is the restraint layer, which is interwoven to distribute tremendous loads evenly and efficiently around its torus, much in the same way as the reeds in a round basket are woven to spread weight and give the basket strength. Each strap is made of Kevlar ®, an aramid-fiber material, which has a very high strength-to-weight ratio and great impact resistance, and is often used today in the making of bulletproof vests. Woven together into the vehicle's main shell, these straps when inflated form a system that is capable of withstanding up to 4 atmospheres of pressure differential (over 54 psi) between interior and exterior.
Inside the restraint layer, multiple bladders of heavy, flexible plastic are mounted to hold in the air. Although only one bladder is necessary to do the job, the requirements for safety in spacecraft design are so high that TransHab's designers put in three bladder layers to protect the vehicle in case one of them failed. On the outside of the restraint layer, a shield of impactresistant layers separated by open-cell foam is mounted to defend TransHab against the tiny meteor-like particles that are often encountered in space, traveling at velocities up to 7 kilometers per second. The outermost layer of the shell is made of a glass fiber cloth that resists abrasion by the charged particles in Earth's ionosphere .
Why Was TransHab Considered for the International Space Station?
TransHab is designed around human requirements, not just engineering solutions to the challenges of spaceflight. It is roomy and offers enough stowage space to take care of a crew for over six months, and it houses all the crew activities from sleeping to exercise. This reduces clutter and activity elsewhere on the International Space Station, enhancing the environment for the scientific experiments that are the station's primary purpose.
For the Human Exploration of Mars
TransHab could also play an important part of the human exploration of Mars or other bodies in the solar system. Without an inflatable module such as TransHab, the cost of getting a crew safely to a remote destination such as Mars could be much higher, and if the alternative is a constricted, conventional spacecraft, the crew would be much more likely to experience stress before the most challenging part of their mission begins on Mars. This makes TransHab a central part of NASA's Mars Design Reference Mission (DRM), as the crew habitat for the journey between planets. At the beginning of the DRM, TransHab is launched in a space shuttle bay, deflated, and packaged tight; once in orbit it can be unfolded, inflated, and deployed. At that time, elements that served structural functions during launch are reconfigured to serve as walls, partitions, and furnishings.
All of this is possible because it is specifically designed for use in a microgravity environment, so its pieces are lighter than other modules. Once ready to go, TransHab would be attached to the propulsion and guidance systems that take it and its crew on the six-month trip to the Red Planet. When they reach Mars, the crew would "park" TransHab in orbit and take a transfer ship to the surface, where their surface habitat is already in place and waiting for them. At the end of their 425-day scientific expedition on Mars, the crew would then launch back up to orbit and reboard TransHab for the journey home.
see also Habitats (volume 3); Human Missions to Mars (volume 3); International Space Station (volumes 1 and 3); Long-Duration Spaceflight (volume 3); Mars Missions (volume 4); Human Factors(volume 3).
Constance M. Adams
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